The invention relates to nonwoven fabrics possessing light stability, particularly ultraviolet, and water barrier properties, suitable for substrates used to manufacture outdoor covers. In particular, the invention relates to nonwoven fabrics having at least one meltblown layer and two spunbonded layers, where each layer includes a base resin combined with at least two hindered amine light stabilizers, hydroxyl amine and phosphite processing aids; and a carrier resin of polypropylene, polyethylene or a mixture of both.
Nonwoven fabrics possessing light stability (particularly ultraviolet) and having water barrier properties are desirable for use as substrates to manufacture outdoor covers. Outdoor covers include marine, automobile, bike and recreational vehicle covers. Such covers include protecting the vehicle from wear and tear caused by wind, rain and sunlight.
Nonwovens and nonwoven composites for such covers are available in the market. One class of such nonwoven web laminates is commonly referred to as spunbonded/meltblown/spunbonded (SMS) laminates. These SMS laminates generally consist of nonwoven outer layers of spunbonded polyolefins and an interior layer of meltblown polyolefins.
Representative of SMS laminates known in the art include U.S. Pat. No. 4,374,888 to Bornslaeger discloses an SMS fabric suitable for use as a recreational fabric in the manufacture of tents, outer garments, tarpaulins and the like. As well as U.S. Pat. No. 5,939,341 to Brown which discloses separate spunbond and meltblown layers of thermoplastic polymers containing a hindered amine light stabilizer and calcined mixed oxides.
In general hindered amine light stabilizers (HALS) are known in the art. For example, published European patent application EP 0792911 A2 to Tennesen discloses a phosphate based flame retardant combined with alkoxyamine functional hindered amine light stabilizer (NOR-HALS) used to achieve flame retardant properties that are better than those with phosphates alone.
U.S. Pat. No. 5,393,812 to Haley describes fibers and fabrics, as used clothing, upholstery and carpeting which contain about 0.01 to 3% (preferably 0.2 to 1.0%) by weight of the composition, of a light stabilizer. This patent discloses a polyolefin, a NOR HALS (alkoxy amine functional hindered amine light stabilizers) and a phosphorous flame retardant (col. 2 line 33-40; col. 4 line 62-64). Regular HALS (hindered amine light stabilizers) may be employed additionally or in place of NOR HALS.
U.S. Pat. No. 5,096,950 to Galbo discloses numerous N-OR1 alkoxy hindered amine light stabilizers.
U.S. Pat. No. 5,200,443 to Hudson discloses a nonwoven web of polypropylene polymer containing an acetylated hindered amine light stabilizer and a hindered amine substituted siloxane.
U.S. Pat. No. 5,004,770 to Cortolano; U.S. Pat. No. 5,124,378 to Behrens; and U.S. Pat. No. 5,300,647 to Malherber all disclose formulations of particular hindered amine light stabilizers.
Although HALS are known none of the art has disclosed the synergistic effect of combining at least two hindered amine light stabilizers to produce a nonwoven fabric having ultraviolet light stability, enhanced water barrier properties and enhanced durability. Thus it is a broad object of the invention to provide a nonwoven fabric with at least one meltblown layer and two spunbonded layers (SMS) having such properties.
Specifically, the fabric layers of the invention are made of a base (or virgin) resin polypropylene combined with melt processing additives. These additives are a mixture of (i) at least two hindered amine light stabilizers (HALS); (ii) processing aids which are either hydroxyl amines or phosphites or a combination of both; and (iii) a carrier resin of either polypropylene or polyethylene or a mixture of both. Pigments are also included in the formulations to impart desired color properties to the resulting fabrics. The additives are incorporated into a base polyolefinic resin to form a homogeneous blend which is then either spunbonded or melt blown and formed into the invention fabrics.
Another object of the invention is to provide a one-step process for producing a spunbond/meltblown/spunbond fabric structure where a first spunbond layer is laid on a moving conveyor belt, at least one meltblown layer of fibers is laid on top of the first layer followed by another spunbond layer. All three layers are bonded in one-step to form the nonwoven fabric.
A specific object of the invention is to provide fabric structures possessing multiple layers of meltblown webs sandwiched between spunbonded webs.
Another specific object of the invention is to provide fabric structures possessing at least one melt blown layer sandwiched between multiple layers of spunbonded webs.
Another more specific object of the invention is to provide nonwoven structures having a useful service life from six to sixty months, depending on the desired end use.
A further object of the invention is to provide a nonwoven fabric that possesses superior water barrier properties over known nonwoven fabrics, particularly spunbond fabrics.
Another specific object of the invention is to provide a nonwoven fabric that possesses superior initial physical properties as measured by grab/strip tensile tests and trapezoidal tear tests.
A further object of the invention is to provide a nonwoven fabric that does not suffer a loss of more than 50% of its initial MD, CD tensiles and initial MD, CD trapezoidal tear values at the end of its useful service life.
A further specific object of the invention is to provide a nonwoven fabric wherein the color shift is maintained within tolerances over the entire service life.
The present invention provides a nonwoven fabric having at least one layer of meltblown fibers sandwiched between two layers of spunbond fibers (SMS). The resulting fabric possessing UV light stability and water barrier properties suitable for use as a substrate to manufacture outdoor covers.
The fabric layers comprise a base resin selected from the group consisting of polypropylene and polyethylene combined with melt processable additives. The melt processable additives are a mixture of (i) at least two hindered amine light stabilizers; (ii) a processing aid selected from the group consisting of hydroxyl amines and phosphites; and (iii) a carrier resin selected from the group consisting of polypropylene and polyethylene. Pigments are also included in the formulations to impart desired color properties to the resulting fabrics.
The base resin and melt processable additives are combined to form a homogeneous blend which is then either spunbonded or meltblown to form the web layers.
The nonwoven fabric of the invention comprises multiple fabric layers. Fabric structures encompassed by the invention include spunbond-meltblown-spunbond (SMS), spunbond-meltblown-meltblown-spunbond (SMMS), spunbond-meltblown-meltblown-meltblown-spunbond (SMMMS), spunbond-spunbond-meltblown-spunbond-spundbond(SSMSS), spunbond-spunbond-meltblown-meltblown-spunbond-spundbond (SSMMSS), spunbond-spunbond-meltblown-meltblown-meltblown-spunbond-spundbond (SSMMMSS) as well as other composite nonwoven fabrics including additional spunbond or meltblown web layers.
Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered with reference to the drawings, which should be construed in an illustrative and not limiting sense as follows: